1. Field of the Invention
The present invention relates to the transmission and reception of television signals in either digital or sampled analogue form. The preferred form of the invention is concerned with the encryption of a multiplexed analogue component (MAC) video signal.
Theoretically, with a digital or sampled analogue signal, the number of encryption methods is almost limitless. However, with video signals of finite bandwidth, care must be taken not to degrade the received picture due to the encryption. For this reason, the present invention proposes to leave unaltered the active picture time and to use the minimum specified by CCIR.
2. Prior Art
In our co-pending application published as International Publication No. WO83/03942 we have disclosed a multiplexed analogue component television signal which is encrypted for transmission and reception by authorised receipients only by dividing the signal into blocks and reordering the blocks prior to transmission. The signal within each block remains in its original order. The preferred arrangement does not split the blocks of analogue signals already present in the MAC signal.
The present invention is an improvement in or modification of the arrangement disclosed in No. WO83/03942 to the extent that it is now conceived that either or both of the original analogue blocks may be cut into a plurality of sections, and the order and/or timing of the commencement of sections altered.
Preferably, only the block containing chrominance signals is split, the block containing luminance signals being unsplit but its position in the line being altered with respect to the original signal.